A collection of 22 studies looking at 16 weather events that occurred in 2013 has come out with a mixed verdict.
The extreme heat waves experienced across Australia, Japan, China, New Zealand and Korea have been attributed clearly to human-induced climate change, while the flooding in many parts is being ascribed largely to the natural variability of the planet's climate.
The peer-reviewed report 'Explaining Extreme Events of 2013 From a Climate Perspective' of studies published by the journal Bulletin of the American Meteorological Society (BAMS) included the heavy rainfall that flooded parts of Colorado, the Australian record heat wave, a blizzard in South Dakota, a storm in Europe, flooding in India and the intense drought in California.
"For temperature there's a very clear signal of climate change that's emerging and has emerged," Peter Stott, a climatologist with the UK Met Office Hadley Centre told Climate Central. For precipitation, there is much larger variability, and "the signal [from climate change] is weaker in many parts of the world compared to the natural variability."
Heat waves in Australia, Japan, China, New Zealand and Korea were found to have a clear climate change-influence.
Research from the ARC Centre of Excellence for Climate System Science (ARCCSS) covering over five different Australian papers found global warming over Australia doubled the chance of the most intense heat waves, tripled the likelihood of heat wave events, made extreme summer temperature across Australia five time more likely, increased the chance of hot dry drought-like conditions seven times and made hot spring temperatures across Australia 30 times more likely.
But when it came to precipitation, the science is still progressing.
A good example of the uncertainty is the case of the Colorado floods. While it is easy to place the blame on a warmer atmosphere that holds more water leading to more rains, according to the BAMS report by Martin Hoerling of the National Oceanic and Atmospheric Administration's (NOAA) Boulder lab, a climate model that compared the preindustrial climate in the region with the current, human-warmed one found no increase in the likelihood of such exceptional rain events.
While a Stanford study found climate change links to the ongoing, three-year California drought, writes National Geographic, another paper by Hailan Wang and Siegfried Schubert of Nasa's Goddard Space Flight Center concludes that "there was no increased risk of drought in California during 2013 as a result of the long-term warming trend."
Summing it up during a press conference, Thomas Karl, director of the NOAA's National Climatic Data Center also said "what this work shows is just what the strengths and limitations we have both in our analyses and our models, which we rely on as tools to help us assess the causes" of events.